Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavior: HTML-only messages are silently converted to plain text, and the attachment payload always includes the attachmentId needed by read_agentmail_attachment. It omits any note on truncation behavior, which lives only in the schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, both front-loaded with the payoff (full body + attachment metadata) followed by the id-retrieval hint. No filler, no restatement of the title.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description must carry the return contract, and it does — body text plus attachment fields. The one gap is that body truncation (maxChars, default 20000) is only discoverable via the schema, and no error behavior (missing message, wrong mailbox) is mentioned.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 67% and messageId carries no schema description; the description compensates by telling the agent where to obtain the id from search_agentmail_messages. mailbox and maxChars are already documented in the schema, so no further gain is claimed there.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Read one message in full') and enumerates exactly what comes back: text body plus attachment name, type, size and attachmentId. It also implicitly separates itself from get_agentmail_thread and search_agentmail_messages by naming the latter as the id source.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly routes the agent to search_agentmail_messages to obtain the required messageId, which is actionable pre-call guidance. It does not, however, state when to prefer this over get_agentmail_thread (full thread vs single message), so the alternatives story is incomplete.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.